The capacity of hoisting installations has become a problem when loads are hauled over sunk shafts. No increases in the capacity of drum-type hoists can be achieved without significantly increasing the size and mass of the drums and reduction gears. Largesize equipment requires much space underground which must be cut and maintained eventually. The haulage and installation of bulky equipment in a mine which is cramped for room may cause difficulties. There is also no special drive in an explosion-proof enclosure which can meet the requirements of a powerful hoist.
Known in the art of hydraulic apparatus for lowering loads which incorporates a platform connected by means of a rope and sheaves to a counterweight in the form of a piston which travels up and down in a hollow column filled with a hydraulic fluid (cf. USSR Inventor's Certificate No. 159,269, IPC B 66 B 19/00).
Since the piston is heavier than the platform, this rises into the topmost position of its own accord on being unloaded. For lowering a load, a throttle valve is used to dissipate the energy of the hydraulic fluid which is formed during an upward motion of the piston under the action of the loaded platform. The known apparatus cannot lift the loaded platform. Moreover, the energy accumulated in the hydraulic fluid is lost irretrievably throught the throttle valve, and much of the hydraulic fluid is also lost due to leaks along the rope which passes through the top cover plate of the hollow column. No high pressure can therefore be maintained in the hydraulic system and the capacity of the apparatus is consequently low.
Also known is a hoisting apparatus a platform whereof is linked to a counterbalancing piston which is set into motion inside a cylinder due to the pressure of a hydraulic fluid (cf. U.S. Pat. No. 2,222,685, 187-17). The piston is much heavier than the loaded platform which consequently rises due to the weight of the piston. The platform lowers when the piston rises in the cylinder acted upon by the pressure.
The capacity of this apparatus is decided by the weight of the counterbalancing piston. An increase in the weight entails an increase in the overall dimensions of the cylinder, its bore and mass.
Further known is a hoisting apparatus comprising hydraulic cylinders which are installed vertically in a shaft and are connected to each other and to a pump by hydraulic lines (cf. USSR Inventor's Certificate No. 588,177, IPC B 66 B 9/04). Each of the cylinders has a hollow body, filled with a hydraulic fluid under a pressure, and a piston which is connected to a hoisting cage by a rope passing through a sealing means outside the cylinder. The sealing means is made up of throttle bushings with restrictive clearance and a leak off manifold connected to the inlet into the pump.
The hoisting cages are lifted and lowered by admitting the hydraulic fluid into the piston rod ends and opposite ends of the hydraulic cylinders, respectively, and building up pressure therein.
The known apparatus suffers from inadequate sealing of the hydraulic cylinders. Hydraulic fluid losses occur through the throttle bushings when a pressure differential is being applied thereto and due to the transport of fluid by the rope, some of the lost fluid adhering to the surface of the rope due to friction and some penetrating into the voids between the wires. The leaks increase with the pressure applied to the hydraulic cylinders and the operating speed of the load handling attachments, substantially reducing the capacity and efficiency of the apparatus.